The present invention relates to a system for recycling a used plastic material, and more particularly to a recycling system which enables revival of a physical property of a used plastic material, and quality assurance of a reclaimed plastic.
In addition, the present invention relates to a method for reprocessing a used ABS (acrylonitrile/butadiene/styrene) resin and a reclaimed ABS resin, preferably relates to a method for reprocessing a used ABS resin, which improves a used ABS resin in impact strength by incorporating thereinto an unused or used ABS resin having such a physical property feature that the impact strength is high, enabling a reclaimed resin to be used in an application which requires the same or higher physical property, and a reclaimed ABS resin obtained by the method.
In recent years, from the viewpoint of saving resources and protecting the environment, various proposals of recycling of materials have been made. Laws concerning recycling, including Home Appliance Recycling Law, are established, and a variety of techniques and systems for recycling plastics have been proposed.
As a conventional way of reuse of plastics, for example, utilization of a used plastic as a fuel or a blast furnace reducing material (Japanese Patent No. 3095739) for the purpose of energy recovery, namely, so-called primary utilization is frequently made. Recycling of waste as materials is mainly performed in general-purpose applications, such as building materials and utensils for daily use. The reason for this resides in that the plastics salvaged are difficult to separate from one another and the physical properties of the plastics deteriorate due to the mechanical or thermal experience in the remolding, so that the plastics salvaged cannot be reused in the application similar to the application in which the original products are used. On the other hand, recycling of a plastic as a functional resin containing a reclaimed plastic has been realized; however, the utilization rate in this recycling is as low as about several tens %. The utilization rate is a value determined by the following formula.Utilization rate (%)=(Weight of reclaimedplastic)/{(Weight of reclaimed plastic)+(Weight of originalplastic)}×100
Another reason for difficulty of the recycling of plastics as materials is that used plastic materials are difficult to constantly obtain. The products on the market have different needs and colors, and therefore plastic materials of the same type in a satisfactory amount are difficult to obtain, and the plastic materials cannot be strictly separated from one another, thus making the quality assurance difficult.
A recycling system has been proposed in which recycling treatments for individual parts constituting a product are collectively controlled from the stage of raw materials to the final stage of disposal of the product to utilize the reclaimed plastics in the same product (Japanese Patent Application Publication No. 2000-181958). However, this system is unprofitable and difficult to apply to general-purpose resins. In addition, a problem in that the reclaimed plastic cannot always be desirably colored is pointed out, and thus this system has a problem in that the system is difficult to apply to the products being on the market or currently used.
ABS resins are widely used in the production of inexpensive, durable products. The ABS resins have high durability and hence are used as basic materials in the production of parts for products, such as computer housings, television sets, and automobiles. Recently, as we are becoming increasingly environmentally conscious, in addition to metal materials which have conventionally been recycled, recycling and reuse of petrochemical products are more vigorously attempted. Laws, such as recycle, waste law, and Containers and Packaging Recycling Law, have been established, and hence, in the product groups of large-size household appliances, automobiles, and the like, recycling of plastics is being promoted. However, in the above recycling of plastics, thermal recycling using the plastic as a heat source, or recycling for cascade utilization in which lowered physical properties of the reclaimed plastics are not a fatal problem is mainly conducted. Needless to say, the ABS resin is not an exception.
The reason that the above-mentioned recycling method is mainly employed in the recycling of plastics resides in that a change with time during the use of the plastic or mixing of foreign matter or heat experience during the recycling of the plastic causes the reclaimed plastic to have physical properties lowered, thus making recycling of the plastic as a material (material recycling) difficult. However, for more effectively utilizing used plastics, material recycling is preferred. Therefore, various studies have been made on the material recycling of plastics. The present inventors have found that, by adding to a used resin a resin different from the used resin, the used resin can be prevented from suffering quality deterioration or can be improved in the quality, and they have previously filed a patent application (Japanese Patent Application No. 2001-093981).
As mentioned above, conventionally, in the recycling of plastics, especially in the material recycling, there have been technical problems, e.g., (a) a problem of the lowering of physical properties including strength, (b) a problem in that the utilization rate is low, that is, the content of the reclaimed plastic in the recycled product is low, and (c) a problem of color in that there is the limitation of changing the color of the reclaimed plastic from a pale color to a dark color, thus making it difficult to color the reclaimed plastic with a desired color.
In view of the above, it is the first object of the present invention to provide a collective recycling system for used plastic materials, including collection and separation of resins and selection for reuse, which system can solve or improve the above problems, and further can be widely applied to general-purpose resins, such as products which are on the market or currently used.
On the other hand, ABS resins generally have excellent physical properties, such as tensile strength, flexural strength, and impact strength, and are relatively inexpensive, and hence used in a wide variety of household appliances and the like. Therefore, the ABS resins are one of resins demanded to be recycled as materials, and various studies have been made on the technique for reprocessing ABS resins including a method for separating plastics.
The present inventors have made various studies on the technique for reprocessing ABS resins. Physical properties of a reclaimed ABS resin were measured and compared with the physical properties of an unused ABS resin. As a result, it has been found that, in the physical properties, especially the impact strength is markedly lowered. The impact strength as a physical property is the most unique feature of the ABS resin, and is a very important property in the selection of the resin as a material, as compared to the other physical properties. Specifically, the ABS resin has high impact strength, and therefore, generally, the application in which the ABS resin is used requires excellent impact strength. In the reuse of the ABS resin, when the reclaimed ABS resin is difficult to use in the application which requires high impact strength, the application of the reclaimed ABS resin is limited, so that the cost for recycling is increased, leading to a failure to promote material recycling of the ABS resin. Therefore, in the method for reprocessing the ABS resin, the improvement of the impact strength is an important task.
Further, another task of the use of the reclaimed resin is coloring of the resin. In the use of the reclaimed resin in various parts for products, especially in the use of the reclaimed resin in the original application (part), coloring of the reclaimed resin with a desired color is required. However, in recycling of the ABS resin, it is difficult to color the reclaimed resin with a desired color while reviving the physical property, e.g., impact strength as mentioned above.
In view of the above, it is the second object of the present invention to enable a used ABS resin to be reclaimed and reused in the application which requires excellent physical property, for example, the original application or the application similar to the application in which the ABS resin is used.